Capnography-Guided

Vadim Pinskiy*, Neil Mori*, Harsh Shah*, Poonam Dudhat*, Glen Atlas# *Stevens Institute of Technology, Biomedical Engineering / Hoboken, NJ 07030 #Dept. of , University of and Dentistry of New Jersey / Newark, NJ 07103

Abstract—The device uses to guide intubation for more effective . The concentration is conveyed to the anesthesiologist through an audible signal, which is used to direct the endotracheal tube into the . The process significantly speeds up procedure time in difficult airway cases while reducing the risk of improper placement.

I. INTRODUCTION A. Background Intubation is a commonly performed in which an artificial airway is established in a patient to provide proper . It depends on the proper insertion of the endotracheal tube into the trachea instead of the . The placement of the endotracheal tube into the esophagus can lead to death, brain damage, of the stomach, II. PRELIMINARY STUDY damage to the and does not correct the improper gas A preliminary study was performed on 12 patients by Dr. exchange. Improper placement of the endotracheal tube can be Atlas of the Anesthesiology Department at the University of difficult to detect and dramatically increases the intubation Medicine and Dentistry of New Jersey (UMDNJ) to confirm procedure time, often leading to complications. This problem feasibility of the design. The results showed that aspired CO2 is significantly magnified in difficult airway cases such as from tracheal had a mean of 23.25 those involving trauma or anatomical obstructions. mmHg with a standard deviation of 14.01 mmHg. Whereas

Capnography is the of the concentration of esophageal intubations had a mean aspCO2 partial pressure of exhaled carbon dioxide in order to assess the physiologic 2.25 mmHg with a standard deviation of 2.06 mmHg (P = status of patients with acute respiratory problems. Up to now, 0.0036). The design immediately differentiated between the capnography was primarily used after the insertion of the trachea and the esophagus, resulting in a much faster endotracheal tube into the body to verify the position of the intubation. ET tube. Though effective, the process is quite time consuming, requiring the complete retraction and reinsertion III. DESIGN of the tube to change the location. The proposed device integrates a mainstream capnograph, a suction unit, and an audio circuit to obtain a direct B. Objective measurement of CO2, which is conveyed to the physician The purpose of the proposed device is to give physicians, through a dynamic audio circuit. For a standard 7.0 mm , and other airway management personnel the diameter endotracheal tube, an applied suction of 180 mmHg, ability to better manage difficult airway cases by using a turbulent airflow of 0.5 liters/second is generated with a capnography to guide the intubation. By providing real-time corresponding Reynolds number of 9,375, ensuring the CO2 feedback, the intubator will know immediately when the extraction of a sufficient gas sample quickly. The 180 mm Hg ET tube has entered the trachea (aspCO2 >5 mmHg) or the is critical to the proper functionality of the device. If the esophagus (aspCO2 <5 mmHg) and can take immediate action applied pressure is significantly greater then 180 mmHg, to correct the position of the tube. The primary application of physical damage to the , trachea, or esophagus this device will be in difficult intubations, where the airway could result. If it is significantly lower, an insufficient sample pathway is obstructed by a large wound, fluids, tumor, or any will be extracted, resulting in a false reading. other major abnormality that prevents conventional intubation. The CO2 concentration of the extracted gas is measured by As a result, overall procedure time is shortened and the risk of a pre-calibrated infrared detector within the capnograph, this an esophageal intubation is greatly reduced, saving money, data is then relayed to the rest of the system through a voltage time, and lives. converter. The entire system will operate from a single 120

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AC power source and/or a single built-in battery, with an expected operating time of about 4 hours. The entire package will be portable, lightweight and rugged, ideal for hospital and pre-hospital settings.

A. Measurement Mainstream capnographs function by using an infrared sensor to scan a small volume of gas, which is analyzed to determine the partial pressure of CO2. The capnograph selected for this design, unlike side-stream capnographs, had an external infrared detector which was positioned on the proximal end of the endotracheal tube, rather then inside the IV. TESTING main unit. Combined with a suction unit, this feature allows The preliminary testing of the device will be performed for real-time data acquisition. The vacuum pump of the unit is using laboratory means to test the response of the device to attached to the capnograph sensor and provides enough different levels of carbon dioxide at the distal end of the suction to deliver sufficient gas from the end of the ET tube to endotracheal tube. A two pump system will be used to obtain the proper mixture of and carbon dioxide, the flow of the capnograph sensor for a proper CO2 concentration measurement. The suction unit is small enough to be the mixture will be closely regulated to resemble that of the incorporated into the base of the capnograph. The low power trachea. consumption of the suction unit allows it to be incorporated After IRB approval at UMDNJ, the device will be tested into the main power supply of the capnograph during actual intubations to ensure the optimal operating conditions. A laptop-based data acquisition system will be B. The Audio Circuit used to track and record the performance and output of the To streamline the intubation process, an audio circuit was device. The laptop system will be operated independently of the device by a technician with no connection to the intubator. designed to correlate the concentration of aspired CO2 to the pitch of the projected sound. The change in pitch varies with Adjustments in the volume, quality and pitch sensitivity of the audio circuit will be adjusted based on the result of the study each incremental increase in the CO2 concentration; a difference of even 5 mmHg can easily be detected by an untrained professional. Guided by the pitch of the sound, the ACKNOWLEDGMENT intubator will be able to make real-time adjustments in the This project was greatly helped and would not be possible position of the ET tube as to increase the pitch and guide the without the assistance and guidance of Dr. Arthur Ritter and tube into the trachea. In future models, the volume and audio Professor Vikki Hazelwood of the Chemical, Biomedical and output can be adapted to accommodate most environmental Materials Department at Stevens Institute of Technology. Dr. conditions. Stuart Tewksbury of the Electrical and Computer Engineering Department was also a great inspiration and assisted the group C. Operation on countless of occasions with seemingly impossible circuit The device is operated by activating and calibrating the diagrams. We would also like to thank the staff of the capnograph using the built-in optical infrared standards. The Anesthesiology Department at the University of Medicine and suction unit is then connected to hollow stylet. A sterilized ET Dentistry of New Jersey – New Jersey Medical School. tube is then connected to the infrared detector of the capnograph. The stylet is then inserted into the proximal end REFERENCES of the ET tube, creating a closed path from the ET tube to the [1] G. Atlas, "Development, Characterization, and Initial infrared detector and the suction unit. When the intubator is Assessment of Capnography-Guided Intubation". Canadian ready to perform the procedure, the suction unit is activated Journal of , Volume 51(A44). June 2004. and the intubation is performed normally, except the intubator relies on the audio signal for any position adjustment. The [2] SD. Mentzelopoulos: "Capnography-guided nasotracheal audio circuit is calibrated to initially produce a low audible intubation of a patient with a difficult airway and unwanted respiratory depression". Anesthesia and Analgesia, Volume pitch correlating to a low CO2 reading of normal atmospheric air and assuring the intubator that the device is properly 87(3). September 1998. 734–736. working. Upon entering the trachea, the sound will change to [3] LH. Wolf: "Capnography during fiberoptic a higher pitch in response to the increase in CO2 concentration, indicating that the ET tube is properly to verify tracheal intubation". Anesthesia and Analgesia, positioned and ready to be fixed in place. The stylet is then Volume 85(3). September 1997. 701–703 removed and discarded, along with the tubing of the suction unit.

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